Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Semiconductor devices perform a wide range of functions such as analog and digital signal processing, sensors, transmitting and receiving electromagnetic signals, controlling electronic devices, power management, and audio/video signal processing. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, diodes, rectifiers, thyristors, and power metal-oxide-semiconductor field-effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, application specific integrated circuits (ASIC), power conversion, standard logic, amplifiers, clock management, memory, interface circuits, and other signal processing circuits.
A semiconductor wafer includes a base substrate material and plurality of semiconductor die formed on an active surface of the wafer separated by a saw street. FIG. 1a shows a conventional semiconductor wafer 10 with base substrate material 12, active surface 14, and back surface 16. Conductive through silicon vias (TSV) 18 are formed through semiconductor wafer 10 and electrically connected to circuits on active surface 14.
Many applications require the semiconductor die to be reduced in height or thickness to minimize the size of the semiconductor package. FIG. 1b shows a grinding operation with grinding wheel 20 removing a portion of back surface 16 of semiconductor wafer 10 and reducing the thickness of the semiconductor wafer to about 100 micrometers (μm). Grinding wheel 20 is controlled to leave edge support ring 22 between side surfaces 26 and 28 of the remaining base substrate material 12 around a perimeter of semiconductor wafer 10 for structural support. Grinding wheel 20 reduces the thickness of semiconductor wafer 10 in an interior region or wafer grinding area 24 of the wafer within edge support ring 22.
In FIG. 1c, a conductive layer 30 is formed on surface 32 after the grinding operation. Conductive layer 30 includes a plurality of interconnect pads electrically connected to conductive TSV 18 and the circuits on active surface 14. Conductive balls or bumps 34 need to be formed on conductive layer 30 for electrical interconnect. A ball drop process using stencil 36 is a possible technique to distribute bumps 34 onto the interconnect pads of conductive layer 30. Stencil 36 is typically made of metal for stiffness with openings 38 aligned with the interconnect pads of conductive layer 30. Bumps 34 would be deposited over stencil 36 and a brush or shaker causes the bumps to drop into openings 38. Ball drop works if surface 32 is planar and the stencil makes contact with the planar wafer surface. However, if stencil 36 with openings 38 is disposed over edge support ring 22, the separation between openings 38 and the interconnect pads would not achieve the proper placement of bumps 34 on the interconnect pads. Bumps 34 would drop through openings 38 and be randomly dispersed over surface 32. Accordingly, stencil 36 is ineffective in forming bumps 34 over the interconnect pads of conductive layer 30 with edge support ring 22.
A thin semiconductor wafer is susceptible to warpage without support. FIG. 1d shows a warped thin semiconductor wafer 10 without the edge support ring. Stencil 40 is placed over semiconductor wafer 10. The warped condition of semiconductor wafer 10 creates space between openings 42 and surface 44. Surface 44 is not planar in warped semiconductor wafer 10 and portions of stencil 40 do not contact the surface. Bumps 46 would again drop through openings 42 and be randomly dispersed over surface 44. Accordingly, stencil 40 is ineffective in forming bumps 46 over the interconnect pads of conductive layer 30 with a warped semiconductor wafer 10 without an edge support ring.